Hi Noadi! Sorry for the delay--I posted a long reply yesterday, but apparently it got eaten by my computer or the website or something. On the bright side, it will probably be more coherent as a result of rewriting from memory this morning. =)

I'm glad you brought up the Fry paper. We had a really interesting discussion in my lab when that came out. In their Introduction, the authors assert that blue-ring tetrodotoxin is fabricated in-house by endosymbiotic Vibrio bacteria. While that could be true, no one in my lab, including a post-doc who's studied TTX for years, has ever seen evidence for it. And the paper itself doesn't cite any references for that claim. That grievance cast a bit of a pall over the rest of the paper, though it is an interesting study. I was also somewhat irked by:

Several cephalopod species have been confirmed to use envenomation as a mechanism to neutralize captured prey and/or as a defense against predators (Norman and Reid 2000).

Norman and Reid 2000 is a popular field guide to the cephalopods of Australia. I have tremendous respect for Mark Norman as a scientist, I love this book, and my copy of it is well-worn, but it isn't peer-reviewed literature. It would be more appropriate for them to cite the actual research papers that described envenomation in the first place.

And, incidentally, in their introductions to each cephalopod sub-taxon, Norman and Reid only mention envenomation in octopuses. Since I've had this book for a long time, it may be one of the reasons I had it in my head that octopuses were the only toxic cephalopods. Which is, in fact, wrong!

But the counterexamples do not come from Fry's paper, because they didn't find any toxins. They found DNA that codes for proteins that are similar to other proteins that are known to be toxic in other animals. They are well aware of this limitation. Their concluding sentence:

Further work into the bioactivity of these proteins will be illuminating with regard to their functional diversity and role in predation.

That means their study didn't address bioactivity--toxicity--of the proteins. They couldn't, because they didn't look at the proteins, just the DNA. I expect at least some will turn out to be toxic; we just don't know yet.

By comparison, in 2008 this Japanese research group studied toxicity of proteins from the salivary glands of six non-octopus cephalopods: three cuttlefish and three squid. All were toxic againt crabs, some were toxic against mice. Spooky!